System for transferring a load from ship-based production and storage units to dynamically positioned tankers

ABSTRACT

A system for transferring a load from ship-based production and storage units ( 10 ) to dynamically positioned tankers ( 3 ), comprising a loading hose ( 14 ) which, during a loading operation, extends between an end ( 11 ) of the ship-based unit ( 10 ) and a bow manifold ( 6 ) on the tanker ( 3 ), and which is stored on the ship-based unit ( 10 ) when not in use. The ship-based unit at said end is provided with two manifold and connecting means ( 12  resp.  13 ) located on either side of the fore-and aft axis (X-X) of the unit ( 10 ), and the ends of the loading hose ( 14 ) are arranged for connection to a respective one of the connecting means ( 12, 13 ), so that the hose, in connected condition, can hang like a catenary between the connecting means ( 12, 13 ) transversely to the ship-based unit ( 10 ), and an optional end of the hose ( 14 ) can be released from the connecting means in question, to be connected to the bow manifold ( 6 ) on the relevant tanker ( 3 ).

[0001] The invention relates to a system for transferring a load fromship-based production and storage units to dynamically positionedtankers, comprising a loading hose which, during a loading operation,extends between an end of the ship-based unit and a bow manifold on thetanker, and which is stored on the ship-based unit when not in use.

[0002] In connection with offshore loading of oil from so-called FSO andFPSO vessels, i.e. vessels for floating storage of oil (FSO=FloatingStorage and Offloading) and for floating production and storage of oil(FPSO=Floating Production, Storage and Offloading), it is advantageous,especially in exposed ocean areas, to use DP-based buoy loading tankers(DP=dynamic positioning) in order to maintain a high continuity/loadingregularity also in periods of bad weather.

[0003]FIG. 1 of the drawings schematically shows how ship and equipmenttypically is arranged to carry out such operations. The figure shows aship-based storage and/or production unit 1 (i.e. an FSO or FPSO vessel)which is anchored by means of a turret anchoring 2, for example aso-called STP buoy, and a DP buoy loading tanker 3, wherein a loadinghose 4 for the transfer of oil extends between the rearward end 5 of theunit 1 and a bow manifold 6 and an associated mooring arrangement on thetanker 3. The prevailing weather direction is designated “W” in theFigure.

[0004] The loading hose 4 typically is stored on a large hose reel 7 onthe FSO/FPSO vessel 1 when the buoy loading tanker is not moored to thevessel.

[0005] The distance L1 between the tanker 3 and the vessel 1 typicallyis about 80 m. The distance between the vessels to some extent isdelimited by the length of the hose 4. This is, inter alia, due to thefact that a long hose will require a larger hose reel 7, and also astronger winch equipment on board the buoy loading tankers. When thetanker 3 is loading, the loading hose 4 hangs like a catenary betweenthe vessel 1 and the manifold 6 on the tanker.

[0006] It is to be remarked that the DP-operated tanker 3 very often isconnected to the FSO/FPSO vessel 1 lying in front by means of a mooringhawser 8, as shown in FIG. 1. The mooring hawser is stored on a hawserwinch 9 on the vessel 1. The function of the mooring hawser is toprevent the hose 4 from being overloaded in cases wherein the distancebetween the vessels unintentionally becomes too large.

[0007] Traditionally, the mooring hawser 8 normally is placed in theregion around the centre or fore-and-aft axis of the FSO/FPSO vessel, asillustrated in FIG. 1.

[0008] Experience shows that such DP loading is a very efficient loadingmethod under marginal weather conditions. For example, a DP tanker willbe able to carry out loading operations in waves having a significantwave height of H_(s)=5.5-6 m, as compared to a corresponding wavelimitation of H_(s)=3.5-4 m for ships without DP.

[0009] However, it has occurred several times that DP ships move aheadin an uncontrolled manner. This type of occurrence, which is consideredto be very critical since a contact or collision then might occurbetween the two vessels, is referred to in the field as “position dropout”. Therefore, there is a need for a system which reduces the risk ofpossible damage effects in case of an occurring “position drop out”.

[0010] Thus, it is an object of the invention to provide a loadtransferring system which reduces to a substantial degree the risk ofcontact/collision between the moored vessels during a loading operation,and which also gives the possibility of reducing the damage extent if acontact/collision nevertheless should occur.

[0011] A further object of the invention is to provide such a systemwhich involves a simplification of the equipment forming part of theload transferring arrangement.

[0012] For achievement of the above-mentioned objects there is provideda system of the introductorily stated type which, according to theinvention, is characterised in that the ship-based unit at said end isprovided with two manifold and connecting means located at either sideof the fore-and-aft axis of the unit, and that the ends of the loadinghose are arranged for connection to a respective one of the connectingmeans, so that the hose, in connected condition, can hang like acatenary between the connecting means transversely to the ship-basedunit, and an optional end of the hose can be released from theconnecting means in question, to be connected to the bow manifold on therelevant tanker.

[0013] The invention will be further described below in connection withan exemplary embodiment with reference to the drawings, wherein

[0014]FIG. 1 shows a schematic plan view of the above-mentionedpreviously known system;

[0015]FIG. 2 shows a schematic view of the rearward end portion of anFSO/FPSO vessel which is equipped with a system according to theinvention;

[0016]FIGS. 3 and 4 respectively show a side view and a view seen fromastern of the end portion of the vessel in FIG. 2, with associatedsystem equipment;

[0017]FIG. 5 shows a view of the loading hose forming part of thesystem; and

[0018]FIG. 6 shows a schematic plan view of an FSO/FPSO vessel and aDP-operated tanker during a loading operation with the system accordingto the invention.

[0019] FIGS. 2-4 show an FSO or FPSO vessel 10 wherein a systemaccording to the invention is arranged at the rearward end 11 of thevessel. As shown, the system comprises two manifold and connecting means12 and 13, respectively, which are situated on either side of the centreor fore-and-aft axis X-X of the vessel. A loading hose 14 extendsbetween and is connected to the connecting means, the ends of theloading hose being provided with connecting units for connection to arespective one of the connecting means 12 and 13, so that the hose inthe illustrated connected condition, when loading does not take place,can hang like a catenary between the manifold and connecting means 12,13, transversely to the vessel 10, as shown in FIG. 4. Thus, in thiscase the hose is not pulled in onto a hose reel on the FSO/FPSO vessel,as in the above-mentioned known solution.

[0020] As shown in FIG. 5, the loading hose 14 at each end is providedwith connecting units in the form of a coupling head 15 which isconnected to the hose via a swivel unit 16 allowing rotation of thehose. The coupling heads are of the standardized type which is alsosuitable for connection to the bow manifold on the relevant tankerswhich are to use the system. Thereby it is indifferent which end of theloading hose is connected to the tanker.

[0021] Each end of the hose 14 is also shown to be provided with alifting bridle 17 for use in hoisting of the hose end in question, forconnection to the relevant manifold and connecting means.

[0022]FIG. 6 illustrates a loading operation wherein a DP-based tanker 3is connected to the vessel 10 via the loading hose 14.

[0023] When the DP tanker 3 arrives, one can decide whether it isoptimal to undertake connection on the port side or starboard side ofthe vessel 10, indicated as loading position I and loading position IIin FIG. 6. The connection essentially takes place in the traditionalmanner in that a messenger line (not shown) is first transferred fromthe vessel 10 to the tanker 3. By means of this messenger line theloading hose 14 is then pulled over to the talker and is connected tothe bow manifold 6.

[0024] If, during a loading operation, there should occur anunintentional “position drop out”, or that the ship for other reasonsmoves ahead in an uncontrolled manner, the tanker, when it is connectedin the respective loading positions on the port an starboard side, willmore easily be able to manoeuvre laterally, so that contact/collisionwith the vessel 10 is avoided. This is illustrated by arrows A in FIG.6.

[0025] When the loading operation has been carried out, the hose end inquestion is disconnected from the bow manifold of the tanker 3, and thehose end is pulled automatically back to the vessel 10 and is connectedto the free connecting means. For this purpose the vessel 10 is equippedwith a winch (not shown) and a handling line 18 forming part of each ofthe connecting means 12 and 13 on the vessel.

[0026] It is to be remarked here that the loading hose 14 in the presentsystem in a simple manner will be able to be adapted with a somewhatlarger length than if the hose is stored on the deck of the FSO/FPSOvessel. This is due to the fact that it will be more easy to pull intowards the tanker a hose which already hangs down into the sea. It istherefore supposed that the distance L2 between the two vessels in thepresent system advantageously will be able to be increased to typically100 m.

[0027] An increased distance to typically 100 m will, in combinationwith the novel hose arrangement, also contribute positively to secureagainst contact/collision between s the two vessels. The use of asomewhat longer hose will also reduce the necessity of using a mooringhawser, as described in connection with the solution according toFIG. 1. Thereby the disconnecting procedure is simplified, and the timerequired to carry out a disconnection, is reduced. With the presentsystem it will typically be possible to disconnect the hose in a safemanner in ca. 15 seconds if a critical situation should occur. Whenusing a mooring hawser, the disconnecting time will be more than 20seconds.

[0028] Since the loading hose is connected to the manifold systems onthe starboard and port side of the FSO/FPSO vessel when the hose is notin use, one will, with a suitable piping, be able to empty the hose ofoil when it is in the connected, stored position. For example, this maybe carried out by pressurizing the hose from one side. Alternatively,one may flush the hose clean after emptying, by pumping water throughthe hose.

[0029] The above described arrangement will be practically useful inconnection with replacement of the loading hose and its equipment. Otherknown load transferring systems require that the loading hose isconnected to the tanker in order to be able to carry out suchoperations.

[0030] As shown in FIGS. 2-4 and 6, the vessel 10 at its rearward end 11is also provided with a special fender structure 19. This fenderstructure is designed to protect both the load transferring system, i.e.the loading hose 14 with associated equipment, and the primary structureof the vessel 10. As shown, the fender arrangement 19 projects asubstantial distance outwards from the vessel 10, both at the rearwardend and in each of the rearward side portions, and is provided withsuitable openings 20 through which the end portions of the hose arepulled up for connection to the connecting means 12 and 13. The roundedshape of the fender arrangement entails that the tanker 3 in case of apossible contact with the vessel 10 will slide along the fenderarrangement and apply a reduced impact energy to the structure.

1. A system for transferring a load from ship-based production andstorage units (10) to dynamically positioned tankers (3), comprising aloading hose (14) which, during a loading operation, extends between anend (11) of the ship-based unit (10) and a bow manifold (6) on thetanker (3), and which is stored on the ship-based unit (10) when not inuse, characterised in that the ship-based unit (10) at said end (11) isprovided with two manifold and connecting means (12 resp. 13) located ateither side of the fore-and-aft axis X-X of the unit (10), and that theends of the loading hose (14) are arranged for connection to arespective one of the connecting means (12, 14), so that the hose, inconnected condition, can hang like a catenary between the connectingmeans (12, 13) transversely to the ship-based unit (10), and an optionalend of the hose (14) can be released from the connecting means inquestion, to be connected the bow manifold (6) on the relevant tanker(3).
 2. A system according to claim 1, characterised in that the loadinghose (14) at each end is provided with a coupling head (15) which isconnected to the loading hose via a swivel unit (16).
 3. A systemaccording to claim 2, characterised in that each of the coupling heads(15) is of a standardized type suitable for connection to the bowmanifold (6) on the relevant tanker (3).
 4. A system according to one ofthe claims 1-3, characterised in that the ship-based unit (10) isprovided with a messenger line, for transferring the relevant end of theloading hose (14) to the tanker (3), for connection to the bow manifold(6) thereof.
 5. A system according to one of the preceding claims,characterised in that the ship-based unit (10) is provided with a winchand an associated handling line (18) for pulling in the free end of theloading hose (14) after disconnection from the bow manifold (6) of thetanker.
 6. A system according to one of the preceding claims,characterised in that the ship-based unit (10) at said end (11) isprovided with a fender structure (19) which is designed so that aconnected tanker (3) will slide along the fender structure (19) in caseof a contact with the ship-based unit (10). Please add the following newclaims 7-15:
 7. A system according to claim 2, characterised in that theship-based unit (10 is provided with a messenger line, for transferringthe relevant end of the loading hose (14) to the tanker (3), forconnection to the bow manifold (6) thereof.
 8. A system according toclaim 3, characterised in that the ship-based unit (10 is provided witha messenger line, for transferring the relevant end of the loading hose(14) to the tanker (3), for connection to the bow manifold (6) thereof.9. A system according to claim 2, characterised in that the ship-basedunit (10) is provided with a winch and an associated handling line (18)for pulling in the free end of the loading hose (14) after disconnectionfrom the bow manifold (6) of the tanker.
 10. A system according to claim3, characterised in that the ship-based unit (10) is provided with awinch and an associated handling line (18) for pulling in the free endof the loading hose (14) after disconnection from the bow manifold (6)of the tanker.
 11. A system according to claim 4, characterised in thatthe ship-based unit (10) is provided with a winch and an associatedhandling line (18) for pulling in the free end of the loading hose (14)after disconnection from the bow manifold (6) of the tanker.
 12. Asystem according to claim 2, characterised in that the ship-based unit(10) at said end (11) is provided with a fender structure (19) which isdesigned so that a connected tanker (3) will slide along the fenderstructure (19) in case of a contact with the ship-based unit (10).
 13. Asystem according to claim 3, characterised in that the ship-based unit(10) at said end (11) is provided with a fender structure (19) which isdesigned so that a connected tanker (3) will slide along the fenderstructure (19) in case of a contact with the ship-based unit (10).
 14. Asystem according to claim 4, characterised in that the ship-based unit(10) at said end (11) is provided with a fender structure (19) which isdesigned so that a connected tanker (3) will slide along the fenderstructure (19) in case of a contact with the ship-based unit (10).
 15. Asystem according to claim 5, characterised in that the ship-based unit(10) at said end (11) is provided with a fender structure (19) which isdesigned so that a connected tanker (3) will slide along the fenderstructure (19) in case of a contact with the ship-based unit (10).